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The Moving Coll Galvanometer, !ikAII', , P~:rnlillnrnl rl1ilt(Jle'I, , •, Undonn radlaJ, , magncuc Octd, , The moving coil galvanometer(MCG) consists of a coil, with many turns, free, to rotate about a fixed axis , In a uniform racUal magnetic field. There is a, cylindrical soft iron core which not only makes the field radial but also, increases the strength or the magnetic field., When a current flows through the coil. a torque acts on it, T, , = NI AB--------(1), , The magnetic torque NIAB tends to rotate the coil. A spring Sp provides a, counter torque., T, , = kcj, - - - - - ( 2 ), , \vhere k is the torsional constant or the spring; Le. the restoring torque per, unit twist, cj, is the deflection is indicated on the scale by a pointer attached to the, spring., In equilibrium,, k<I> = NI AB --····-····(3), , 4' = (N:B) I, The quantity in brackets is a constant for a given galvanometer., ct, o:: I, Thus the deflection produced in the coil is directly proportional to the, current through the coil.

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Current Sensitivity of the Galvanometer, Current sensitivity of the galvanometer is defined as the deflection per unit, current, , ~=, , (N:8), , A convenient way for the manufacturer to increase the sensitivity Is to, increase the number of turns N., , Voltage sensitivity oftbe galvanometer, Voltage sensitivity of the galvanometer ls defined as the deflection per unit, vo ltage., , !V =(NAB).:=, (NAB).:, k, V, k, R, !_=, V, , (NkAB)J.R, , Increasing the current sensitivity may not n.ecessarily lncrease the voltage, sensitivity., If N-+ 2N, i.e., we double the number of turns, then current sensitivity,, ! = (ZN, 2 _t, I, , AB)-+, , k, , I, , Thus, the current sensitivity doubles., If N -+ 2N, then R-+ 2R then the voltage sensitivity,, , != (2NAB)...:..=, (NAB)!.=!, k, 2R, k, R, V, , V, , Thus, the voltage sensitivity remains unchanged ..